Network providers, like AT&T, are continually working to improve network efficiency. Consider a typical transmission from a calling party to called party in which voice signals, accompanied by noise, are transmitted. The noise component considered in this application is primarily the background noise of the speaking party. During this typical transmission there are periods of time when the calling party is not speaking but the background noise is still present. Even though no voice signal is being transmitted, the network is still committing the same amount of resources, and transmitting solely the noise signal. Conventional technology has made the network more efficient by reducing the amount of resources allocated to such a transmission during periods of “silence,” i.e., when only a noise signal is present, so that the bandwidth can be used for other transmissions.
Conventional technology detects a voice signal in a transmission. This technology, referred to as voice activity detection (VAD) or silence suppression (SS), determines whether an input signal is primarily a voice signal or a noise signal based on one or more parameters. This decision may be based on the current frame as well as a few of the preceding frames, to ensure that there is a significant break in the input voice signal. When the VAD/SS technology determines that no input voice signal is being transmitted, i.e., that just noise is present, instead of using a suitable amount of bandwidth for the particular transmission, the VAD/SS technology informs the receiving end that no signal is going to be transmitted. The VAD/SS technology sends one or more bits, referred to as silence insertion descriptors, that are noise characteristics. The VAD/SS technology, instead of transmitting the noise, or the “lack of voice” over the bandwidth, allocates the bandwidth to another use. At the receiving end, the silence insertion descriptors are converted into a representation of the background noise, also known as comfort noise, representation and transmitted to the called party.
In the event that the silence period continues for some time, and there is no significant change in the background noise, then the comfort noise is continually generated. However, if there is a change in the background noise, new silence insertion descriptors will be transmitted to the receiving end. This process avoids a comfort noise that is constant for the benefit of the listener.
Although there is bandwidth savings with this technology, suppressing silence in a transmission has another associated characteristic. Suppressing the silence “degrades” the quality of the connection. The parties participating in the transmission become familiar with each voice and the associated background noise. During periods of silence when the silence suppression system either transmits no signal or silence insertion descriptors, the parties will hear a difference in background noise, i.e., either no noise at all or a slightly different background noise. Noise pumping refers to the different sounds created when switching between the presence of noise and absence of noise. Noise contrast refers to the different sounds created when switching between the presence of actual noise and the presence of comfort noise. As noted above, the comfort noise results when the silence insertion descriptors are converted into a noise signal, and this noise is generally not identical to the actual noise. Both the noise pumping and the noise contrast yield audible distinctions that are apparent and undesirable to the parties.
Network providers, like AT&T, are interested in using network bandwidth efficiently. This is especially important where bandwidth is limited, such as sub-oceanic fiber cable transmissions given the large cost to place the cable. Network providers are also interested in providing the best quality transmissions possible. Thus, given the foregoing, there is a need in the industry to maintain the bandwidth savings using silence suppression techniques while improving the quality of the signal to the users.